Catheters are often positioned in the vascular system of a patient for long-term drug infusion or fluid aspiration. A problem with leaving a catheter positioned in the vascular system of a patient for a long duration is that thrombosis occurs at the distal end of the catheter lumen where there is even a small amount of retrograde blood flow into the catheter. In the vascular system, blood clots form quickly and thrombosis obstructs a catheter lumen over time. A thrombotic obstruction makes the catheter lumen useless and creates a risk for the patient. If a catheter lumen is only partially obstructed by thrombosis and fluid is injected therethrough, a thrombus is flushed loose from the catheter lumen and flows through the vascular system to a narrow diameter site. As a result, the loose thrombus potentially causes an undesirable obstruction in a small or narrowed vessel of the vascular system. If the thrombus obstructs a small vessel in the lung, heart, or brain, serious complications such as pulmonary embolism, heart attack, or stroke may result.
One approach to preventing retrograde fluid flow into a catheter lumen is the use of a catheter having sufficient rigidity for introduction into tissue to provide epidural anesthesia. The rigid catheter includes several longitudinal slits in the catheter wall about the distal end thereof. A limitation of this rigid catheter is that it is not flexible or pliable for atraumatic introduction through the tortuous vessels of the vascular system.
Another approach to preventing the retrograde blood flow that causes thrombosis is the use of a closed end, silicone catheter with a single, linearly extending, two-way slit valve near the distal end thereof. The slit valve is contiguous with the silicone rubber catheter wall, which is treated with dimethylsiloxane for weakening the wall adjacent the valve. A problem with the use of this slit valve is that the valve is positioned on the circumference of the catheter wall. The sides of the slit valve are inadequately supported by the adjacent, curved catheter wall. The inadequately supported sides of the slit valve fail to form a watertight seal and, as a result, permit leakage. Another problem with the use of this slit valved catheter is that the catheter wall adjacent the valve is weakened by dimethylsiloxane, which further decreases support for the slit valve. As a result, the valve is susceptible to improper or crooked closure and retrograde blood leakage. Furthermore, the weakened catheter wall makes the slit valve more fragile and susceptible to damage in repeated operation. In addition, the weakened wall potentially causes collapse of the slit valve against the opposite inner wall of the catheter, thereby preventing use of the valve for aspiration.
Yet another problem with the use of this silicone, slit valved catheter is that the catheter has a smooth exterior surface without a traverse protrusion. As a result, the slit valve is positioned on the circumferential periphery of the catheter adjacent or possibly abutting a blood vessel wall. During irrigation, fluid flow is flushed out of the slit valve and directly against the intimal layer of the blood vessel wall. This fluid flow deflects off the blood vessel wall and creates turbulence in the blood vessel lumen, thereby loosening particles of plaque and other deposits from the blood vessel wall. The loosened particles flow through the vascular system and present the risk of obstructing a small or partially occluded blood vessel. As previously discussed, undesirable obstructions can cause pulmonary embolism, heart attack, or stroke in a patient. During aspiration, the blood vessel wall is potentially drawn against and possibly into the slit valve. As a result, the blood vessel wall can be traumatized and damaged, which causes thrombosis and other cell proliferation and deposition to occur and subsequently obstruct the catheter or blood vessel. Again, trauma to the blood vessel wall loosens plaque and other deposits therefrom and presents the risk of undesirable obstructions as previously discussed.
Yet another problem with this catheter is that the size of the catheter and the durometer of the catheter material must be designed to meet the needs of a particular valve design. This significantly limits the inside and outside diameters of the catheter along with the wall thickness. The durometer of the catheter material can be utilized to change the dimensions of the catheter to meet a particular valve design; however, the range of catheter dimensions and material durometer is still limited.